Vision is limited by nature. Man is limited and so are his faculties. How limited is vision of objects on the ground and how far into the distance can human vision see?
A person who has a herd of sheep, goats or cattle must separate ma'aser from the animals born in the year. These animals are sacrificed in the Temple and their meat is eaten by their owners as kodoshim kalim. A person whose herd increased by less than ten animals is exempt from ma'aser. The Mishnah (Bechoros 54b) explains that even someone who has two herds does not have to combine them and if ten were not born in either one of them, he is exempt from ma'aser, even if the animals born number ten or more altogether. The verse in Yirmiyahu (33:13) states that the time will come when a person would own so many sheep that their owner would not be able to count them on his own. There is therefore a need to determine when two groups of animals are called one or two herds.
The Mishnah says: "Ma'asar beheimah is combined by the distance of the feet of a grazing animal and how much is 'the feet of a grazing animal?' 16 mil." The Gemara 54b explains that Chazal received the tradition that a shepherd can see to the distance of 16 mil and therefore all the eligible animals within this distance mil is considered one herd as the shepherd can stand in the middle and see all the animals.
Many halachos influenced by Chazal's definition of the field of vision:
Husband lost at sea
The Gemara (Yevamos 115a). If a man is lost at sea where the edge of the water is beyond sight (“waters that have no end”), the man’s wife remains prohibited. We must be concerned that the husband might have surfaced beyond our vision and that he is still alive. Rashi there explains that the range of sight is one parsa in each direction, which is only four mil, less than the range of sixteen mil cited in our Gemara.
Based on a comment of Rashi in Eiruvin (8a), Sefer Harei Besamim suggests that there is a difference between the extent of sight on land, which is sixteen mil, and on sea, which is four mil.
Sh’vus Yaakov explains that the Gemara in Yevamos is discussing a case where we not only have to be able to see someone at a distance, but we also have to be able to see whether the person is alive or dead. While it may be possible to see sheep up to a distance of sixteen mil, it is only possible to see if a man lost at sea is still alive up to four mil.
Chut HaMeshulash explains that a person can certainly see beyond one parsa, which is four mil. The verse in Bereshis (13:15) speaks about Avraham Avinu who was told to look across the land, and he was promised, “I will give you the land which you see.” However, the Gemara in Yevamos is not just speaking about the ability to peer across a landscape, but it is speaking of being able to see a specific person or item. This can only be dependably done up until four mil.
Sukka
The Gemara in Sukka (2a) reports that schach of a sukka which is higher than twenty amos is not valid. The verse says that the purpose of dwelling in a sukka is in order that we realize that G-d housed us in sukkos in the desert when we departed from Egypt. When schach is above twenty amos, a person sitting in the sukka does not notice that he is under the schach, because his eyesight does not perceive the roof above that height. Yet, our Gemara says that a person can see up to sixteen mil. This question was posed by R’ Yitzchak Tzvi Levinzon to the Imrei Emes, and he answered that a person can see up to twenty amos even without paying attention. However, when one pays close attention and has specific intent, he is able to see much farther.
Tearing one's garments on seeing the site of the Temple
HaGaon Rabbi Moshe Feinstein zt"l mentions this field of vision also when he was asked by someone from whose windows one can see the site of the Temple if, when he comes to the Western Wall, he should tear his garments according to the halachah of someone who hasn't seen the site of the Temple for 30 days or, since he sees it from afar, he doesn't have to tear his garments. The author of Igros Moshe replied (O.C., III, 85) that if his home is within 16 mil from the site of the Temple, he doesn't have to tear his garments as he is considered as seeing the site of the Temple.
The Mishnaic mil is based on the Latin mile, a distance equivalent to 1000 steps. This is the same as the distance of 2000 amah, which was used in the laws of eiruvin, and today is estimated between 960 and 1200 meters.
Forming a minyan in a field
Teshuvas Minchas Yitzchok was asked about people who daven in the summer in a field, how far apart they could be spread and still constitute a minyan. Does the matter depend upon whether they could see one another, whether they could all hear the sh’liach tzibbur or perhaps they have to stand within four amos of one another since the pasuk (Devarim 23:15) indicates that a person’s camp is four amos. He responded that combining for a minyan depends upon two factors. The first prerequisite is that everyone must be able to hear the sh’liach tzibbur. This is based on Shulchan Aruch’s ruling that if nine people do not listen to the sh’liach tzibbur it may be that the berachos recited by the sh’liach tzibbur are berachos l’vatalos. The second prerequisite is that the participants in the minyan have to be capable of seeing one another. This is based on Pri Chadash’s ruling that when two groups of people are in different rooms they combine to make a minyan if some of them could see one another. Although there are authorities who disagree, in the case of an open field all opinions would agree since there is no wall dividing the group into two that seeing one another is sufficient for them to combine. Sefer Imrei Devash also wondered whether the discussion in our Mishnah has bearing on the question of how far apart a group of people may be spread out and still constitute a minyan. Perhaps they can be as far apart as sixteen mil since they should be able to see one another but perhaps forming a minyan follows a different set of rules. He leaves the matter unresolved.
An eiruv in Manhattan
When an eiruv was arranged in Manhattan, New York, HaGaon Rabbi Moshe Feinstein zt"l was asked to discuss the topic from many halachic aspects (Responsa Igros Moshe, O.C., I, 139). One aspect concerns the approach of the Rishonim which contends that it is impossible to surround an immense area with one eiruv but that the area covered by an eiruv is limited to the area visible by a person standing at its center. As this area is 32 mil, as mentioned by our mishnah (a shepherd can see for 16 mil can utilize an area of 32 mil), Rabbi Feinstein postulates: "Perhaps such an area does not exist in Manhattan" and nothing prevents us from including all of it in the eiruv.
A beracha on seeing a cemetery
Similarly, the poskim discussed the topic of seeing a cemetery, that someone who sees it must bless "asher yatzar eschem badin" (Shulchan 'Aruch, O.C. 242:12). The author of Betzel HaChochmah contends (III, 40) that one who sees the tombstones from a distance of 16 mil must also pronounce this berachah.
Different measurements for the field of vision
If we search the Torah and Talmud for the human field of vision, we also find different definitions than that of our mishnah. Hagar, Sarah's maidservant, furthered herself from her son Yishmael "like flights of an arrow" to avoid seeing his death and two flights of an arrow are merely one mil (2000 cubits, Bereishis Rabah, Vayeira 53:13). The Gemara in Chagigah 20b asserts that from a distance of a mil a person cannot determine if impurity touched his workers. He who accompanied the kohen who sent off the goat to Azazel stood at a mil distance from him to see him (Yoma 67a). The obvious conclusion is that the field of vision mentioned by our sugya does not mean vision which discerns details but that objects within 16 mil from a person do not blend with the background but stand out (see Piskei Teshuvah, published in Poland about 80 years ago, I, 167, who remarks about the apparent contradictions in the said Gemaros).
Raising goats and sheep
The Yerushalmi explains (Bava Kama 7:7, Pesachim 4:3) that one must not raise sheep or goats in an area greater than 16 mil because the shepherd must notice where his animals are to prevent them from stealing food from neighboring fields. Of course, this distance was fixed according to the human field of vision, and the shepherd often stands at the edge of his flock (Piskei Teshuvah, ibid, and in Nefesh Chayah, O.C. 688, S.K. 2).
Who does the horse save (or cast a shadow)?
We conclude with the unique comment of the Rogatchover Gaon zt"l on the statement of Rabbi Yehoshua ben Levi (Pesachim 50a), that "HaShem will in the future add to Yerushalayim till the distance where a horse runs and is matzil – casts a shadow". Rashi (s.v. 'Ad sha'ah) explains that this concerns a horse which began to run in the morning from Yerushalayim and that Yerushalayim will expand to the place where the horse will get to at midday when his shadow under him. The author of Tzafnas Pa'neiach explains (in the Hashmatos to Hilchos Ta'anis, 5:16) that this means a horse intended to save those condemned to death (matzil means "saves" and "casts a shadow"). This horse stood at a distance of 16 mil from the beis din so that if the beis din cancelled the death penalty of a person taken already to the place of execution, they signaled the horse's rider to rush to the executioner to inform him. This is the meaning of sus hamatzil.
